Employees of Lawrence Livermore National Laboratory have ported Sun's/Oracle's ZFS natively to Linux. Linux already had a ZFS port in userspace via FUSE, since license incompatibilities between the CDDL and GPL prevent ZFS from becoming part of the Linux kernel. This project solves the licensing issue by distributing ZFS as a separate kernel module users will have to download and build for themselves.

"So please, give me a real reason why people should choose BtrFS over ZFS (particularly given ZFS is still a few years ahead of BtrFS in terms of testing and development).

A real reaseon is indeed the same as not using NTFS - it doesn't really work well with my platform of choice, while btrfs is definitely getting there. There will never really be a choice between the two. In the end it's btrfs vs. ext4 vs ext3, really. "
You've still not answered my question and furthermore, NTFS is used extensively because of Windows - so that's a terrible example.

I couldn't give a toss about your personal platform of choice. You made a statement that ZFS was going to die and I want you to provide evidence to back up your opinion. Thus far all you've done is spout yet more personal opinion.